1. Field of the Invention
The present invention relates to a metering device to measure current flowing through the human body, and more specifically relates to a metering device to measure current which would flow through the human body upon physical contact with an item carrying radio frequency, electromagnetic fields.
2. Description of the Prior Art
To reduce the potential for radio frequency (RF) shock and burns, safety guidelines with respect to human contact with items carrying radio frequency, electromagnetic fields require measurements of these contact currents. These measurements are required to ascertain whether the contact currents are lower than maximum permissible exposure values as set forth in the safety guidelines.
Limits on contact currents to reduce the potential for RF shock and burns have recently been proposed by the International Radiation Protection Association (IRPA) of the World Health Organization (WHO), in Canada and other foreign nations such as the United Kingdom. In the United States, the Institute of Electrical and Electronics Engineers (IEEE) C95.1- 1991 Standard has determined guidelines for contact currents which would flow through a human body to ground based on the condition of grasping an item carrying radio frequency, electromagnetic fields. The RF current (averaged over any one second) through an impedance equivalent to that of the human body should not exceed the following maximum permissible exposure (MPE) values: EQU I.sub.MPE =1000.times.f mA for 0.003.ltoreq.f.ltoreq.0.1 MHz EQU I.sub.MPE =100 mA for f&gt;0.1 MHz
where f is the frequency in megahertz (MHz).
For simultaneous exposure to electromagnetic fields at several frequencies where contact currents will exist for each of the frequencies, the proposed guidelines are that the fraction of the square of the contact currents in terms of I.sup.2.sub.MPE should be determined for each of the frequencies and the sum of all such fractions should not exceed unity. This can be written as follows: ##EQU1##
Due to the health hazards as determined by the previously mentioned organizations in the United States and abroad, with respect to human exposure to the potential for RF shock and burns, it is necessary for employers to monitor workers who are exposed to such hazards. Therefore, there is a need for a reliable, portable, accurate metering device for measuring contact current which would flow through the human body when physical contact is made with an item carrying radio frequency, electromagnetic fields. The metering device will let the operator know whether the current exceeds the maximum permissible exposure values as set forth in the proposed safety guidelines.